Integrated circuits are very complex devices that include multiple layers. Each layer may include conductive material and/or isolating material while other layers may include semi-conductive materials. These various materials are arranged in patterns, usually in accordance with the expected functionality of the integrated circuit. The patterns also reflect the manufacturing process of the integrated circuits.
Integrated circuits are manufactured by complex multi-staged manufacturing processes. This process may include depositing photo-resistive material on a substrate or layer, selectively exposing the resistive material by a photolithographic process, and developing the photo-resistive material to produce a pattern that defines some areas to be later etched or otherwise processed. After the pattern is processed various materials, such as copper are disposed. The deposition step is usually followed by a removing access material, such as chemical mechanical polishing (CMP). The polishing can result in various deformation, such as dishing and erosion.
Various metrology, inspection and failure analysis techniques evolved for inspecting integrated circuits both during the manufacturing stages, between consecutive manufacturing stages, either in combination with the manufacturing process (also termed “in line” inspection techniques) or not (also termed “off line” inspection techniques). It is known that manufacturing failures may affect the electrical characteristics of the integrated circuits. Some of these failures result from unwanted deviations from the required dimensions of the patterns.
X-ray reflectivity (XRR) and X-ray florescence (XRF) are methods that use X-rays to determine the thickness of thin films. Various vendors sell metrology tools that utilize these methods for thin film thickness determination. One of these vendors is Jordan Valley Ltd. of Israel that sells various tools. The JVX5200 metrology tool implements both methods.
These X-ray based methods can also be utilized for detection of voids within thin films. A brief description of the state of the art may be found in the following patents and patent applications, all being incorporated herein by reference: U.S. Pat. No. 6,556,652 titled “Measurement of critical dimensions using X-ray” of Mazor et al., U.S. Pat. No. 6,535,575 titled “Pulsed X-ray reflectometer” of Yokhin, U.S. Pat. No. 6,041,095 titled “X-ray fluorescence analyzer” of Yokhin, U.S. Pat. No. 6,389,102 titled “X-ray array detector” of Mazor et al., U.S. patent application 2003/0156682 titled “Dual-wavelength X-ray reflectometry” of Yokhin et al.
X-ray spot is relatively large. For example, the JVX5200 tool can produce a spot of about 18-30 micron when implementing XRF, and a larger spot (due to grazing angle illumination) that has a length of about 2-8 millimeters when implementing XRR. These measurements require relatively large test pads (about 70×100 micron for XRF and 100-150×2000-5000 microns for XRR).
Electron beam metrology and defect detection tools, such as Scanning Electron Microscopes are used for high resolution measurement of surface features as well as surface defects and contaminations. These tools generate a spot of electrons that is very small. Typical spots may have a length of about few nanometers. These electron beam metrology and defect detection tools are not able to detect voids or measure the thickness of layers, such as oblique layers and especially of copper layers.
U.S. patent application Ser. Nos. 10/242,496, 09/990,170 and 09/990,171 of Nasser-Ghodsi et el. titled respectfully, “methods and system for dishing and erosion characterization”, “Methods and system for defect localization” and “methods and system for void characterization” also provide a description of prior art methods and systems for analyzing copper films.
U.S. patent application Ser. No. 09/990,171 of Nasser-Ghodsi describes an system and method that provides an indication about the presence of voices in response to the measurement counts. It is noted that said count based system and method are prone to various errors resulting from measurement inaccuracies, such as difference between measurements, different X-ray absorption and emission characteristics by different materials.